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Abstract: We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15kOe) and the ab-plane α ≡∠(H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa2Cu3O7−δ single crystals. We discuss the appearance of low temperature “tails” (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami–Larkin theoretical model of the fluctuation conductivity for layered superconductors. [Copyright &y& Elsevier]

Abstract: The temperature dependence of the transport anisotropy of ReBa2Cu3O7−δ (Re=Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa2Cu3O7−δ , the temperature dependence of the anisotropy of the resistivity ρ c /ρ ab (T) for the HoBa2Cu3O7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity. [Copyright &y& Elsevier]

Evolution of the excess conductivity in YBCO single crystals is investigated after their step-by-step irradiation with fast electrons. The dependence of the coherence length ξ c (0) along the c -axis on the irradiation dose dependence is obtained. It is revealed that an increase of the irradiation dose from 1.4 to 8.8 × 1018 cm − 2 leads to a considerable extension of the temperature range of the excess conductivity. This is accompanied by a factor of about 1.5 increase of ξ c (0) and a shift ot the 2D-3D crossover point in temperature. [ABSTRACT FROM AUTHOR]

• YBCO single crystals are irradiated with fast electrons and annealed in oxygen atmosphere. • The irradiation and annealing lead to a broadening of the superconducting transition. • Resistivity temperature dependence is described by a combination of different conductivity mechanisms. • Annealing allows one to recover the normal conducting properties to the initial, non-irradiated state. The effect of annealing on the conductivity of optimally doped YBa 2 Cu 3 O 7 − δ single crystals irradiated with fast electrons is investigated. The variation of width of the superconducting transition with increase of the irradiation dose and in the course of annealing is associated with the evolution of the sample inhomogeneity. A recovery of the critical temperature T c after annealing to some intermediate value between those in the initial and irradiated states is observed. This recovery of T c is accompanied by a substantial narrowing of the superconducting transition whose width nicely matches that in the non-irradiated state. The observed transition narrowing is attributed to an improvement of the sample homogeneity in consequence of the diffusion-induced growth and eventual coalescence of superconducting domains. In addition, the complete recovery of the normal conductivity after annealing points to a reversible change of parameters of the charge carriers scattering on phonons and defects. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the conductivity in the basis plane of the non-stoichiometric ReBa2Cu3O7−δ (Re=Y, Ho) single crystals. The excess conductivity (Δσ) is described by in the wide temperature range T f < T < T*, where T* is the mean field temperature of the superconducting transition. We determined that the temperature dependence of the pseudogap (PG) is described in terms of the BCS–BEC crossover theoretical model. It is observed that a reduction in the oxygen content leads to the widening of the temperature interval, in which the PG region is realized, and to the narrowing of the area of the ρ(T) linear dependence in the ab-plane. [Copyright &y& Elsevier]